The present invention relates to actuator control for motor driven systems. In particular, it relates to improving performance and accuracy of the actuators.
Motor driven translational systems are used in a variety of electronic devices today. They are used to move mechanical systems under electrical control such as auto-focus systems or optical image stabilization systems in digital cameras, video recorders, mobile phones, personal digital assistants, and other electronic devices. In such systems, a motor driver integrated circuit generates a drive signal to an actuator which, in turn, drives a mechanical system (e.g., a lens assembly, in the case of an auto-focus system). The motor driver generates the drive signal in response to an input that indicates the desired displacement. Integrated circuit chips are widely used to control or drive a variety of actuators such as voice coil (VCM) actuators, shape memory alloy (SMA) actuators, and MicroElectroMechanical System (MEMS) actuators.
Many actuators show a non-linear relation between the amount of voltage applied and the amount of displacement produced. The non-linear response leads to inaccurate performance of open loop motor driven systems. Actuator responses also can vary among manufacturing lots of the same actuator design. Furthermore, operational factors such as temperature and physical orientation with gravitational force have a substantial effect on the actuator responses. FIG. 1 shows example responses of a MEMS actuator in three different orientations. Each plot includes an offset voltage (shown as X0), which is the minimum voltage required to effectuate displacement. Each plot also includes a maximum displacement voltage (shown as Xf); voltages beyond the maximum displacement voltage cause no further relevant mechanical displacement. It is common to obtain significantly different non-linear responses from different actuator devices.
Actuator response variances lead to poor performance thus inefficient actuator systems especially in open loop control situations. Therefore, there is a need in the art that can transform the undesired non-linear responses into accurate linear transform functions usable by the actuator system.